Admin members can manage almost everything in your account.
They can:
View and manage orders
Process order fulfillment
Add, edit, and remove products
Manage shipping settings
Open Reports and download the accounting CSV
Manage coupons and discounts
See financials
Admins can run your account on your behalf with access to nearly all settings as if it was their account. This avoids you having to hand over your password.
Only you and your Admins can open Reports, so make your bookkeeper an Admin if they need your sales figures or the accounting CSV.